Please help me to decide: external HD drive connected to Time Capsule or Nas Drive

Dear all,
I have 4 computers at home, iPads and iPhones. I am currently doing my backups to one Time Capsule of 1Gb capacity and use some USB drives to backup two of the computers.
I would like to concentrate my backups in one drive and am faced to two strategies: connecting a USB drive to my Time Capsule or buying a NAS Drive and connect it to my Time capsule. I would like to be able to access my files ober the Internet, even being out of home.
Which one of the strategies would you recommend? Thank you very much for your help,
gume

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